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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Overview
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Instruments for Optical Fibre Systems
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Optical Power and Loss Testing
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Optical Sources
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Optical Power Meter Fundamentals
Measurement of Optical Power is of fundamental importance in optical systems
Photodiode detectors are normally used in power meters for optical fibre systems.
Large-surface area preferred to ensure detection of all of the light from the fibre.
Photodiode
Optical Fibre
Photodiode
active area
Spot formed on detector
by light from fibre
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Typical Power Meter
Calibrated at 850 nm, 1300 nm and 1550 nm
Measurements in Microwatts, dBm and dBr
(relative dB)
Range +3dBm to -50 dBm (0.001 microwatts)
0.1 dB resolution
Wide range of adapters including ST, FC/PC and
SC
9V battery powered
More sophisticated units have a larger number
of calibrated wavelengths
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Loss Measurement: Length of fibre only
Attenuation for a length of fibre only (connectors not included)
Optical
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Tail
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1. A short reference lead is used for X and the received power P1 is recorded
2. The lead X is replaced by the length of fibre and received power P2 is recorded
3. Attenuation in the fibre length is P1 - P2
4. Fibre length under test and the reference lead must have the same geometry and
connectors from the same manufacturer
5. Most power meters incorporate a dBr (dB relative) function to assist in measurements
Optical connector
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Loss Measurement: Patch-panel to Patch-panel
Setting reference
Making the
measurement
Optical
power
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Optical
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Launch lead
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Patch-panels
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1. A launch reference lead is connected as shown and the optical power P1 is recorded
2. The power P1 represents the power in the launch lead at point A
3. The launch lead from the source is connected to the local patch panel
4. The power meter is taken to the remote patch panel and connected by a reference tail lead
5. The power level P2 is then measured and the loss between A and B is P1 - P2
6. Fibre under test and the reference lead must have the same geometry and connectors for
the same manufacturer
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Optical Time Domain Reflectometry
An Optical Time Domain Reflectometer (OTDR) is an instrument that can display loss in a
fibre link as a function of distance on a screen.
An Optical Time Domain Reflectometer works by transmitting laser light pulses down an
optical fibre and by measuring the reflected light coming back to the OTDR as a function
of time and level.
The OTDR then converts time to distance and from the returned levels the loss at various
distances is estimated
The result is a display of loss versus distance for the fibre.
Coupler
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Basic OTDR
block diagram
Splice
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APD
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Processing
Display
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
What can an OTDR provide?
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Understanding an OTDR Display
Light is reflected back to the OTDR from along the fibre the because of Rayleigh
scattering in the fibre
Much larger reflections occur at joints with small airgaps and at the fibre end or
at a break
Light reflected back from joints, breaks etc.. produces a spike on the display that
looks like "gain". This is not important
Key to diagram:
1. Fresnel reflection from first
connector
2. Back scattered light from fibre
3. Increase in loss at fusion splice
4. Fresnel reflection from fibre end
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Sample OTDR Display
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Zoomed OTDR Display
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Typical OTDR
Wide variety of benchtop, handheld and PC based OTDRs available
Ranges from single km to 100's of km, resolutions from <1 m to 50 m
Cost is still high relative to other instrumentation IR£ 10K and higher
Exfo FTB-300 OTDR
Available at 850, 1310 and 1550 nm
Can be configured with different modules for
LAN to long range distances
Multimode ranges from 0.1 km to 40 km
Singlemode ranges from 625 m to 160 km
Dead zone < than 25 m, Accurate to +/- 1m
Class 1 laser source (eye safe)
ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)
Summary
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ADAPT is a Human Resources Community Initiative supported by the European Union through the European Social Fund (ESF)